This invention relates to a filament wound frame for a game racquet such as a tennis racquet, racquetball racquet, squash racquet, badminton racquet, etc. More particularly, the invention relates to a game racquet frame which is formed by interspersed winding.
Filament winding is a well known process for forming products from filament material such as graphite fiber, glass fiber, etc. In the filament winding process, filament material is wound around a rotating mandrel to form a tube. The filament material can be in the form of a tow, which is formed from a plurality of filaments or continuous fibers, for example, with carbon 3000, 6000, or 12000 filaments per tow. Fewer or more filaments per tow can be used for carbon as well as other fibers, for example, from one to 50,000.
The filament material is coated with resin before or after winding. The wound tube is placed in a mold having the shape of the end product, and the mold is heated to cure the resin.
Filament wound parts are normally manufactured by winding discrete layers of material on a mandrel, using a helical or geodesic path. Each layer is made up of a 2-ply balanced laminate formed from a multicircuit winding pattern. The number of circuits required for each layer is calculated from the bandwidth of the material and the wind angle, so that the pattern closes and a constant thickness is achieved in the layer. Different layers may be wound at different angles, but each layer typically consists of a +.alpha..degree. angle ply and a -.alpha..degree. angle ply with respect to the longitudinal axis of the rotating mandrel, resulting from the reciprocating traverse of the carriage in the winding machine.
Conventional filament winding produces discrete layers or lamina of fibers. The layers have a tendency to move relative to each other when the wound article is stressed, during removal from the mandrel and loading of the wound tube in the mold. Also, the physical properties of the article are often limited by the shear properties between layers, called interlaminar shear.
Tennis racquets have been produced by conventional filament winding. For example, EPO patent publication No. 0 470 896 describes forming a frame for a tennis racquet by winding fibers of glass, carbon, or other materials.
The following definitions are used herein:
CIRCUIT: One complete traverse of the fiber feed mechanism of a filament winding machine. PA1 INTERSPERSE: To sequence wind circuits from two or more patterns in an arbitrary manner as selected by the designer. Each circuit is appied individually such that any combination and sequence of wind angles from the patterns may by applied. No discrete layers or lamina exist. PA1 TOW: Untwisted bundle of continuous filaments PA1 PLY: A single pass on a filament winding machine in which fiber is applied in one direction to the axis of the mandrel. PA1 A LAYER is typically formed from a series of winding circuits resulting in a closed pattern of 2-plies; one of +.alpha..degree. and the other of -.alpha..degree.. PA1 LAMINA: A single ply or layer in a laminate made up of a series of layers.